1. Field of the Invention
The present invention relates to a signal conversion technique, and particularly to an analog/digital converting device for converting analog signals into the corresponding digital signals.
2. Description of the Related Art
As an example of a circuit for converting input analog signals into digital signals, a pipeline A/D converter is known (see Japanese Unexamined Patent Application Publication No. 9-275342, for example). The pipeline A/D converter is formed of multiple signal conversion units one to another, each of which have a function for low-bit analog/digital conversion. With such a configuration, the pipeline A/D converter performs A/D conversion in steps by actions of each signal conversion unit. Also, a cyclic A/D converter has been proposed wherein the output from a signal conversion unit including a subtracting/amplifying output unit is input to the same signal conversion unit as a feedback signal so as to perform A/D conversion multiple times with the same single conversion unit.
In general, each analog circuit block included in a system LSI is designed according to predetermined specifications. Accordingly, development of an analog circuit block according to different specifications requires redesign thereof. Design/development for an analog circuit block requires a great number of steps such as layout and wiring, logic verification, trial manufacturing, and evaluation. In some cases, these steps require several months, leading to a bottleneck problem in development of a system LSI. Development of an analog/digital converter has the same problem, as well. In particular, in rapidly advancing fields such as image processing, communication, and so forth, demand for a high-speed and high-precision A/D converter is increasing, leading to a demand for a technique for reducing development time of such an A/D converter.